(1) Field of the Invention
The present invention relates to the fabrication of LCD integrated circuit devices, and more particularly, to a method of passivating the passivation layer of an LCD integrated circuit device in order to maintain a uniform gap height between the top and bottom substrates.
Liquid crystal displays (LCD) have been used in the art for such applications as computer and television screens. Typically, the topmost level fabricated on a bottom substrate is a series of metal pixels, 19.times.19 microns in area. There are typically 1024.times.768 pixels having a spacing of 0.7 microns between each pixel. The liquid crystal display layer is built on this array of metal pixels and enclosed by a top substrate comprising a transparent material
FIG. 1 illustrates a LCD integrated circuit device of the prior art. Bottom semiconductor substrate 10 is illustrated. First metal lines 22 are formed overlying a barrier/glue layer. An anti-reflective coating (ARC) layer 24 may be formed over the metal lines 22. An insulating layer 26 is deposited over the metal lines. Tungsten plugs 28 are formed within openings through the insulating layer to the metal lines 22. A second level of metal lines 32, usually an aluminum alloy, are formed overlying a second barrier layer 30. The aluminum alloy is separated and protected by a passivation layer, typically 1000 Angstroms of undoped silicate glass (USG) 34 followed by 2500 Angstroms of silicon nitride 36. The liquid crystal material 52 lies between the passivation layer and the top substrate 56.
For good performance, high speed, and sharp display in the LCD, it is critical to maintain a uniform gap between the top and bottom substrate. The crucial gap height is not maintained in the process of the prior art. As seen in FIG. 1, the height A above the metal pixels is not the same as the height B between the metal pixels.
There are a number of patents in the field of LCD's. For example, U.S. Pat. No. 5,696,386 to Yamazaki, U.S. Pat. No. 5,708,486 to Miyakawaki et al, and U.S. Pat. No. 5,868,790 to Curtain et al discuss LCD formations in which the gap width is non-constant. U.S. Pat. No. 5,056,895 to Kahn teaches an insulating leveling layer of polymer or spin-on-glass. U.S. Pat. No. 5,721,601 to Yamaji et al discloses a spin-on-glass planarizing film. U.S. Pat. No. 5,592,318 to Majima et al teaches planarizing with a polyimide resin.